Time delay relay

ABSTRACT

A time delay relay is disclosed in which bimetal snap disc actuators are heated by a PTC heater to cause the operation of an associated switch after a predetermined time delay interval. The bimetal snap discs are supported in metal retaining cups positioned on opposite sides of the heater. The retaining cups function to support the snap discs, position the heater, provide an electrical connection for the heater, and to provide a heat conducting flow path between the heater and each associated disc. In one embodiment, a single snap disc assembly is positioned on each side of the heater. In another embodiment, the assemblies provide two separate bimetal snap discs on each side of the heater.

United States Patent Schmitt [4 1 Nov. 12, 1974 TIME DELAY RELAY [75]Inventor: Donald J. Schmitt, Mansfield, Ohio [73] Assignee: Therm-O-DiscIncorporated,

Mansfield, Ohio [22] Filed: Oct. 15, 1973 [21] Appl. No.: 406,539

[52] U.S. Cl. 337/107, 337/354 [51] Int. Cl. H0lh 71/22 [58] Field ofSearch 337/59, 75, 102, 107, 354, 337/355 [56] References Cited UNITEDSTATES PATENTS 3,489,976 l/197O Marcoux 337/102 3,500,275 3/1970Oravec.. 337/75 3,582,853 6/1971 Morris 337/354 X 3,713,062 l/1973Butler ct al. 337/107 Primary Examiner J. D. Miller AssistantExaminerFred E. Bell Attorney, Agent, or Firm-McNenny, Farrington,Pearne & Gordon [5 7] ABSTRACT A time delay relay is disclosed in whichbimetal snap disc actuators are heated by a PTC heater to cause theoperation of an associated switch after a predetermined time delayinterval. The bimetal snap discs are supported in metal retaining cupspositioned on opposite sides of the heater. The retaining cups functionto support the snap discs, position the heater, provide an electricalconnection for the heater, and to provide a heat conducting flow pathbetween the heater and each associated disc. In one embodiment, a singlesnap disc assembly is positioned on each side of the heater. In anotherembodiment, the assemblies provide two separate bimetal snap discs oneach side of the heater.

13 Claims, 3 Drawing Figures TIME DELAY RELAY BACKGROUND OF THEINVENTION This invention relates generally to relay devices and moreparticularly to a novel and improved time delay relay employing aplurality of bimetal snap disc actuators, in combination with a singlePTC heater.

PRIOR ART It is known to combine a PTC heater and a bimetal snap discoperated switch to provide a time delay relay or sequencer. The US.Letters Pat. No. 3,489,976 discloses such a device. It is also known toprovide a multiple disc device as illustrated in the US. Letters Pat.No. 3,500,275 with a PTC heater to provide a time delay relay in which afirst switch operates after a first time interval, and a second switchoperates after a second and longer time delay interval. In such latterdevice, a single heater element provides two different time delayintervals. In both such known devices, the PTC heater works only fromone side.

SUMMARY OF THE INVENTION In accordance with the present invention, atime delay relay is provided in which one or more bimetal snap discs arepositioned on each side of a PTC heater, so that the heater functionsfrom both sides to operate snap discs selected to provide the desiredtime delay intervals. In the illustrated preferred embodiments, metallicdisc retainers function to position the associated disc, to provide agood heat conducting path between the heater and the associated disc,and also to provide the electrical connections for the heater. In oneillustrated embodiment, a single disc is mounted on each side of a PTCheater. The two discs are each selected to provide a predetermined timedelay. Usually the time delay interval of one disc exceeds the timedelay interval of the other disc.

In a second illustrated embodiment, two bimetal snap discs are locatedon each side of the PTC heater. In this embodiment, there are fourseparate snap discs which are all operated by the single heater. Thevarious snap discs are selected to produce the desired delay intervalwith each disc operating with a different delay than the other discs.Consequently, four separate and distinct time delay intervals areobtained with the second embodiment of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS 'FIG. 1 is a side elevation inlongitudinal section illustrating a first embodiment of this inventionin which a single bimetal snap disc is mounted on each side of a PTCheater;

FIG. 2 is a fragmentary perspective view of one of the disc retainingcups illustrated in FIG. 1; and

FIG. 3 is a side elevation in longitudinal section of a secondembodiment of this invention in which two bimetal snap discs are mountedon each side of the single PTC heater.

DETAILED DESCRIPTION OF THE DRAWINGS Referring to FIG. 1, the firstillustrated embodiment of this invention includes a pair of identicalswitch bodies and 11 each of which supports a switch 12 and 13,respectively. Each of the switches 12 and 13 includes a fixed contactsupport 14 secured to the associated body by a rivet l6 and providing afixed contact 17. A resilient movable contact support 18 is providedwith a movable contact 19 at its outer end which is movable into and outof engagement with the associated fixed contact. The movable contact armis secured to the associated body by a rivet 21 and is electricallyconnected to a terminal member 22.

Identical disc cups 23 and 24 are mounted on the bodies 10 and 11,respectively. A bimetal snap disc 26 is supported in the disc cup 23,and a second bimetal snap disc 27 is supported in the disc cup 24. Eachof the discs is formed with a shallow dished shape and operates to snapback and forth between two positions of stability upon reachingpredetermined calibration temperatures. The switch 12 is operated by thedisc 26 through a bumper 28. Similarly, the switch 13 is operated by thedisc 27 by a bumper 29. The two bumpers are sized with clearance so thateach switch opens and closes after its disc is in snap movement.

Mounted between the adjacent ends of the two disc cups 23 and 24 is aPTC heater 31 which exhibits a relatively low resistance below apredetermined temperature and a sharply increasing resistance above suchpredetermined temperature. Such positive temperature coefficient (PTC)heaters are known to persons skilled in the art and may be, for example,of the type described in the US. Letters Pat. Nos. 3,434,089 or3,489,976. In the illustrated embodiment, the PTC heater is generallycylindrical in shape and has one face 32 engaging the end wall of thecup 23 and its opposite face 33 in engagement with the end wall of thecup 24.

Preferably, the interfaces between the ends of the PTC heater and theend walls of the two cups 23 and 24 are provided with an electricallyand thermally conductive cement 35, such as a conductive epoxy cement toinsure that a good electrical connection is provided at each interfaceand also to insure that a good thermal connection is provided. The cup23 is provided with a tenninal extension 34, and the cup 24 is providedwith a terminal extension 36. The two terminals 34 and 36 are connectedto the source of electrical power for operating the PTC heater 3].

With this arrangement, it is not necessary to provide separateconnecting means to the PTC heater, and each of the cups functions inthree separate manners. Each cup serves to position the associated disc,to conduct heat from the PTC heater to the associated disc, and toprovide the electrical connection for the PTC heater.

In some instances, it may be desirable to provide one or both of thecups 23 and 24 with a spring structure to compensate for variations intolerance of the various parts of the assembly and to insure a goodintimate contact exists between each cup and the adjacent face of theheater. One structure for providing this spring action is illustrated inFIG. 2, wherin the cup 24 is formed with a spring section 41 in its endwall. The spring section is produced by forming two parallel cuts 42permitting the spring section to be deformed beyond 45 through which theterminals 14 and 22 project.

Each of the end caps also provides a side wall 47 shaped to closely fitand support the associated body and 11. The side walls 47 are formedwith an axially extending recess 48 to receive one of the two terminals34 or 36 as the associated body is moved axially to the assembledposition. Mating projections 49 formed on the other end cap projectsalong the recesses to completely close the assembled device. Exceptingalong the recesses and projections, the two end caps abut at theinterface 51. With this structure, two end caps, like the two bodies,can be identical to minimize tooling costs and inventory requirements.In fact, all of the elements in the assembled device, excepting theheater and the two discs, are identical.

The heater, because of its PTC characteristics, initially drawsarelatively heavy current, and therefore, heats rapidly to thetemperature at which the resistance increases. The current thendecreases as the resistance increases with the result that the heatertends to stabilize at a given temperature determined by the resistancecurve of the heater. Such heaters tend to be relatively insensitive tovoltage fluctuation. In order for the discs to operate, it is necessarythat the stabilization temperature of the heater be above thecalibration temperature of the discs.

In practice, the selection of the discs is dictated by thecharacteristics of the PTC heater, the rate of heat transfer from theheater to the discs, and the time delay interval desired. If, in aparticular assembly, a disc with a given calibration temperatureprovides a time delay which is too short, a disc is selected with ahigher calibration temperature to increase the time delay. Conversely,if a given disc provides a time delay which is too long, a disc with alower calibration temperature should be selected to reduce the timedelay.

Normally, the two switches are required to operate at different timedelay intervals. Since in the illustrated embodiment the rate of heatflow from the two sides of the heater is substantially the same, the twodiscs are selected to have two different calibration temperatures.

When the heater is de-energized after the operation of both switches,the switches sequence back to their normally closed position after aperiod of time determined by the operating temperatures of the disc andthe rate of cooling of the entire device. In a given assembly, the timedelay of a particular disc on heating is determined by its uppercalibration temperature, and the time delay on cooling is determined byits lower calibration temperature.

' In the second illustrated embodiment of the present inventionillustrated in FIG. 3, similar switch assemblies are again provided oneach side of a PTC heater 61. In this embodiment, a switch body 62 isagain mounted in an endcap 63, and a switch body 64 is mounted in an endcap 66. The two switch bodies and the two end caps are identical.Further, each of the two assemblies in this embodiment is provided withtwo discs and two switches.

In FIG. 3, the two switch assemblies are illustrated in positions inwhich the left-hand assembly is rotated 90 with respect to theright-hand assembly. Therefore, in FIG. 3, the innermost switch is fullyillustrated on the right-hand side, and the outermost switch is fullyillustrated on the lefthand side. For purposes of explanation, similarreference numerals will be used to designate similar elements on the twoassemblies. A reference numeral without a prime is intended to indicatean element on the right assembly, and the same reference numeral with aprime added, designates the corresponding element on the left assembly.During the initial discussion, reference will be made only to the rightassembly with the understanding that the structure on the left assemblyis identical.

A disc retainer cup 67 is mounted on the body 62, but in thisembodiment, the retainer cup is provided with two shoulders to supporttwo separate bimetal snap discs 68 and 69. The innermost disc 68operates a movable contact support arm 71 through a centrally locatedbumper 72. The bumper 72 extends through an opening 73 in the disc 69and an opening 74 in the movable contact support arm 76. A tubularbumper 77 engages the disc 69 and functions to operate the movablecontact support arm 76.

Each of the innermost switches includes a fixed contact 81 on a terminalmember 82 which is secured in position by a rivet 83. Mounted on thefree end of the movable contact arm 76 is a contact 84. The opposite endof the movable contact arm 76 is electrically connected to a terminal 86and is mounted by a rivet 87.

Referring now to the left-hand side of the figure, each of the outermostswitches includes a movable contact support arm 71 which carries amovable contact 91 at its free end. The contact support arm 71' iselectrically connected to a terminal 92' and is mounted by a rivet 93.The fixed contact 94 of the switch is mounted on a terminal 96 securedin position by a rivet97'.

Here again, the disc caps 67 and 67 of each assembly function to providethe electrical connections for the PTC heater 61, to support theassociated discs, and also to provide heat conduction from'the adjacentinterface of the PTC heater to the associated discs. In this embodiment,however, four separate and distinct time delay intervals are provided'for the operation of the four separate switches. The snap disc 68, forexample, can be selected with a calibration temperature to operate itsassociated switch after a first predetermined time interval while thesnap disc 68' is selected with a different calibration temperature sothat it operates its associated switch after a predetermined timeinterval different than the first predetermined time interval.Similarly, the snap discs 69 and 69' are selected with still otherdifferent calibration temperatures so that their associated switchesoperate with third and fourth time delay intervals. In this embodiment,it is, therefore, possible to use a single PTC heater to operate fourseparate and distinct switches with four separate and distinct timedelay intervals.

In accordance with one aspect of the present invention, a PTC heater iscombined with the two switch assemblies so that each switch assemblyreceives heat from one face of the heater. In its broader aspects, thisinvention also contemplates the use of other types of heaters which donot necessarily provide a PTC characteristic.

It should be recognized that with the present invention, multiple timedelays can be obtained in a simple and reliable manner, and that thecost of manufacture is minimized while good reliability and long-lifecharacteristics are achieved.

Although preferred embodiments of this invention are illustrated, itshould be understood that various modifications and rearrangements ofparts may be resorted to without departing from the scope of theinvention disclosed and claimed herein.

What is claimed is:

1. A relay comprising A. an electric heater,

B. a first assembly positioned on one side of said heater,

C. a second assembly positioned on the opposite side of said heater,

D. each assembly including,

a. a disc retainer, b. a bimetal snap disc supported by said retainer,

c. and a switch operated by said snap disc,

E. each retainer being formed of a material having good electricalconducting properties and good heat conducting properties,

F. said retainers engaging opposite sides of said heater and providingthe electric connection for energizing said heater,

G. said retainers also providing the principal heat flow path betweensaid heater and the associated disc.

2. A relay as set forth in claim 1 wherein said heater is a PTC heateroperable when energized to attain a temperature higher than theoperating temperatures of said discs.

3. A relay as set forth in claim 2 wherein a heat and electricallyconductive cement is provided between each retainer in said heater.

4. A relay as set forth in claim 3 wherein spring means are provided toinsure good contact between said retainers and said heater.

5. A relay as set forth in claim 2 wherein spring means are provided toinsure good contact between said retainers and said heater.

6. A relay as set forth in claim 2 wherein at least one assemblyincludes two snap discs supported in its retainer, and two switches oneof which is operated by each snap disc.

7. A relay as set forth in claim 2 wherein both assemblies are providedwith two snap discs and two switches one of which is operated by eachassociated snap disc.

8. A relay as set forth in claim 7 wherein each disc 9. A relay as setforth in claim 2 wherein each disc is calibrated to provide a time delaydifferent than the 5 time delays of the other discs.

10. A time delay relay comprising A. a PTC heater having oppositesubstantially parallel faces,

B. first and second similar assemblies positioned on opposite sides ofsaid heater with one assembly p0- sitioned adjacent to each of saidfaces C. each assembly including a. a retainer,

b. a temperature responsive element in thermal contact with saidretainer and,

c. a switch operated by said temperature responsive element, and

D. a housing enclosing said heater and said assemblies,

E. each retainer being formed of the material providing good electricalconductive qualities and good thermal conductive qualities,

F. each retainer engaging one of said parallel faces and,

a. providing a connection therewith for energizing said heater, and

b. a conductive heat flow path between said heater and associatedtemperature responsive element,

wherein each assembly includes two temperature responsive elements andtwo separate switches with one of said temperature responsive elementsoperating each of said switches.

12. A time delay relay as set forth in claim 10 wherein said temperatureresponsive elements are bimetal snap discs.

13. A time delay relay as set forth in claim 10 wherein said housing isformed of two similar parts, and said assemblies are similar.

1. A relay comprising A. an electric heater, B. a first assemblypositioned on one side of said heater, C. a second assembly positionedon the opposite side of said heater, D. each assembly including, a. adisc retainer, b. a bimetal snap disc supported by said retainer, c. anda switch operated by said snap disc, E. each retainer being formed of amaterial having good electrical conducting properties and good heatconducting properties, F. said retainers engaging opposite sides of saidheater and providing the electric connection for energizing said heater,G. said retainers also providing the principal heat flow path betweensaid heater and the associated disc.
 2. A relay as set forth in claim 1wherein said heater is a PTC heater operable when energized to attain atemperature higher than the operating temperatures of said discs.
 3. Arelay as set forth in claim 2 wherein a heat and electrically conductivecement is provided between each retainer in said heater.
 4. A relay asset forth in claim 3 wherein spring means are provided to insure goodcontact between said retainers and said heater.
 5. A relay as set forthin claim 2 wherein spring means are provided to insure good contactbetween said retainers and said heater.
 6. A relay as set forth in claim2 wherein at least one assembly includes two snap discs supported in itsretainer, and two switches one of which is operated by each snap disc.7. A relay as set forth in claim 2 wherein both assemblies are providedwith two snap discs and two switches one of which is operated by eachassociated snap disc.
 8. A relay as set forth in claim 7 wherein eachdisc is calibrated to provide a time delay different than the timedelays of the other discs.
 9. A relay as set forth in claim 2 whereineach disc is calibrated to provide a time delay different than the timedelays of the other discs.
 10. A time delay relay comprising A. a PTCheater having opposite substantially parallel faces, B. first and secondsimilar assemblies positioned on opposite sides of said heater with oneassembly positioned adjacent to each of said faces C. each assemblyincluding a. a retainer, b. a temperature responsive element in thermalcontact with said retainer and, c. a switch operated by said temperatureresponsive element, and D. a housing enclosing said heater and saidassemblies, E. each retainer being formed of the material providing goodelectrical conductive qualities and good thermal conductive qualities,F. each retainer engaging one of said parallel faces and, a. providing aconnection therewith for energizing said heater, and b. a conductiveheat flow path between said heater and associated temperature responsiveelement, G. each of said switches providing a pair of separate terminalsextending to a location external of said housing, H. each of saidretainers being provided with a terminal which extends to a locationexternal of said housing.
 11. A time delay relay as set forth in claim10 wherein each assembly includes two temperature responsive elementsand two separate switches with one of said temperature responsiveelements operating each of said switches.
 12. A time delay relay as setforth in claim 10 wherein said temperature responsive elements arebimetal snap discs.
 13. A time delay relay as set forth in claim 10wherein said housing is formed of two similar parts, and said assembliesare similar.